In many portable electronic devices a vibratory alert is used to indicate the occurrence of an event. In a device such as a pager or portable telephone, the vibratory alert is used to silently notify the user of an important event such as the reception of a message. When such a device is worn on the belt of a user, the vibratory alert produces a tactile sensation experienced by the user. In order to assure that the tactile sensation is sufficient to alert the user of the occurrence of the event, it is desirable to maximize the tactile sensation produced by a device such as a pager.
Upon the occurrence of the vibratory alert, the pager forms part of a resonant system. If the frequency of the vibratory alert is not close to the resonant frequency of the resonant system, the tactile sensation experienced by the user may be significantly reduced. Many variables go into determining the resonant frequency of the resonant system, these variables include the place and method of attachment of the pager to the user, the type of clothing worn by the user, physical attributes of the user, and construction variables unique to the pager. With these types of variables, it is virtually impossible to accurately determine the resonant frequency of the resonant system comprising the pager at the time of manufacture of the pager. Thus, it is unlikely that a maximum amount of tactile sensation may be experienced by a user when the frequency of the vibratory alert is set at the time of manufacture of the pager. What is needed is a method for maximizing the tactile sensation due to the vibratory alert responsive to changes in the resonant frequency of the resonant system.
This problem is further compounded by the miniaturization of paging devices. With miniaturization come reduction in the size of a battery supplying the pager with power, and thus a reduction in the power available for generation of the vibratory alert. Thus, what is needed is a vibratory alert having improved tactile sensation without increasing the power drawn to provide the vibratory alert.
Additionally, switching a vibrator on and off at timed intervals, such as for one half second intervals, provides a user of the device with a pleasing and discernable switched tactile alert. Furthermore, the switched tactile alert may reduce the total current drawn from the battery. However, since the switched vibratory alert requires an electrical to mechanical energy conversion, an initial current surge is typically experienced by the battery at switch transitions. Repeated switching off and on introduces repeated current surges on the battery. As the battery nears the end of its life, the current surges may cause other parts of the battery powered electronics in the pager to malfunction. Thus, what is needed is a method of reducing the current surges while providing the pleasing and distinctive switching of the tactile sensation.